The present invention relates to new lubricating compositions comprising mixtures of hydrocarbon oils and ethers of polyols.
Modern lubricating technology has developed a need for increasingly larger quantities of lubricating compositions with good flow properties at low temperatures, which have suitable viscosities at high temperatures and low volatility.
In the field of lubrication of internal combustion engines, "multigrade" oils are used. The multigrade oils are based on mineral lubricating oils containing viscosity index improvers which modify the viscosity index to meet the requirements for classification for service in summer and winter according to the "SAE" classes of multigrade oils.
The behavior of the low viscosity, mineral-oil-base multigrade oils is not entirely satisfactory. The agents used to improve the viscosity index, for example, esters of polyacrylic or polymethacrylic acids are generally mixed with mineral oil bases which have a low viscosity high volatility and insufficient heat stability.
In addition, the viscosity index improving agents are not stable under the shear forces which arise in service.
The viscosity index improving agents have a detrimental effect on the heat stability of the oil. The loss in heat stability is compensated for by an increase in the amounts of inhibitors and dispersant additives which must be incorporated into the lubricating compositions.
Lubricants having a base of bicarboxylic acid esters, such as alkyl esters of adipic or sebacic acid and lubricants having a base of esters of polyols such as pentaerythritol, trimethylol propane or neopentyl glycol with fatty acids having from about 8 to about 16 carbon atoms mixed with mineral oils have been known in the field of lubrication. In general these esters have problems with wear.
The use of liquid polymers of butylenes, isobutylenes or olefins, such as polydecene, for special purposes, in which lubricants free of mineral bases are required, are known. These polymer oils are characterized by low heat stability or unsatisfactory lubricating properties.